Vocabulary

---

Focus : the point under Earth that starts an earthquake

Epicenter : the point that is right under the focus of an earthquake

Seismic waves : traveling vibrations (that travel through Earth)

Primary waves (P waves) : a type of wave from an earthquake that expands and compresses

Secondary waves (S waves) : a type of wave from an earthquake that shakes up-to-down or side-to-side

Surface waves : a wave that forms when S waves+P waves reach Earth's surface

Seismograph : moves the ground up and down or side to side

Magnitude : measurement of an earthquake's strength depending on waves and movement around faults

Mercalli Scale : a machine that rates an earthquake according to their strength

Richter Scale : rates earthquakes according to the size of their seismic waves

Moment Magnitude Scale : rating system that guesses the total power given by an earthquake

Outline

---

Seismic Waves

• P waves
• primary waves
  • are the first to arrive at seismograph station
  • compress or expand the ground
  • buildings: contract and expand
• S waves
• secondary waves
  • reach surface and things start shaking violently
  • cannot move through liquid
  • shakes side-to-side or up-and-down

Detecting Seismic waves
*Seismograph

• records ground movement
• mechanical and electronic types of seismograph
• will show different heights

Measuring Earthquakes

• Mercalli Scale
  • rate earthquakes based on intensity
  • describes earthquakes affecting people,buildings, and land surfaces
  • not a precise measurement
• Richter Scale
  • rating size of seismic waves
  • used for 50 years
  • provides accurate movement even for the smallest earthquakes
• Moment Magnitude Scale
  • rates estimate of total energy produced by an earthquake
  • study data in a seismograph first, then the Moment Magnitude Scale
  • 5.0: small, above 5.0: large

Locating an epicenter

• epicenter
  • farther earthquakes, bigger time
  • draw at least three circles
  • point where circles intercept is the epicenter